Shonen Onmyouji is an interesting departure from what I often see: As a historical fiction, the series is based around the adventures of Abe no Masahiro, the fictitious grandson of the famous and not-so-fictitious Japanese onmyouji, Abe no Seimei. It's a wonder to me why we don't see more shows like this; historical fiction gives a concrete basis for a setting, and even if the series takes the series takes the setting and adds more fantastical elements to it, it still gives the viewer something more to connect to. And with Japan's long and colorful history, there are surely more stories to be told, right?
At the same time, I can appreciate why I don't see more of them, because while Shonen Onmyouji has a strong historical basis, that history isn't one that I - or, I suspect, most of you - am very familiar with. This issue is highlighted by the fact that the series doesn't really make any effort to introduce any of the historical characters or locations to the viewer; they're simply a part of the story from the first minute in. I could call this a flaw, but I won't; this is, after all, a show produced firstly for Japanese audiences. But that doesn't change the fact that if you don't know very much about Japanese history (like, say, who Abe no Seimei was) you'll probably miss out on a lot of the subtleties of the setting.